1. Field of the Invention
The present invention relates to an optical semiconductor device, and more particularly to an optical semiconductor device sealed with an addition curing silicone resin composition.
2. Description of the Related Art
A high-intensity light-emitting diode (LED) having high intensity of light and a large amount of heat generation has been recently produced on a commercial base and extensively used.
Such an LED device is manufactured by using a cup-like premolded package integrally molded with a lead frame, mounting an LED in this package, and sealing it with a sealing resin. At this time, to assure conductivity at the time of mounting the LED and enhance reflection efficiency of the LED, copper is usually used as a base metal of the lead frame, and this material is subjected to silver plating, but there is a tendency of reducing a thickness of the silver plating to decrease a manufacturing cost.
On the other hand, there is a demand for a cured product of a sealing resin to have transparency because of its properties, and an epoxy resin composition made of an epoxy resin such as a bisphenol A epoxy resin or an alicyclic epoxy resin and an acid anhydride based curing agent is generally used (Patent Document 1, Patent Document 2). However, there arises a problem that a cured product of such an epoxy resin composition has low lightfast durability since transmittance for light rays having a short wavelength is low or this material is colored due to light deterioration.
Therefore, as the sealing resin, there has been suggested an addition curing silicone resin composition consisting of an organic compound having at least two carbon-carbon double bonds, which have reactive properties to a hydrosilyl group (SiH group), per molecule, a silicon compound having at least two SiH groups per molecule, and a hydrosilylation catalyst (Patent Document 3, Patent Document 4). However, in a cured product (the sealing resin) of such an addition curing silicone resin composition, there occurs a problem that silver ions are diffused in a thin plated layer, reach a sealing resin layer, and are discolored into brown to deteriorate luminance in a combination with the lead frame having thinly-silver-plated copper, and hence quality of the LED device is lowered. That is, as a current situation, using such an addition curing silicone resin composition does not lead to acquisition of the LED device that suppresses discoloration of a cured product of this resin composition and has excellent durability of reflection efficiency.    Patent Document 1: Japanese Patent No. 3241338    Patent Document 2: Japanese Unexamined Patent Application Publication No. H7-25987    Patent Document 3: Japanese Unexamined Patent Application Publication No. 2002-327126    Patent Document 4: Japanese Unexamined Patent Application Publication No. 2002-338833